Actuators, such as current-controlled, electro-hydraulic valves, are used in vehicles in anti-lock braking systems (ABS), traction control systems, stability control systems, automotive transmissions, and numerous other vehicular systems, as well as non-automotive industrial and commercial products. These valves typically use electrically controlled sliding plungers to selectively permit or prevent fluid flow through the actuator under particular circumstances, as required for the application. The plunger must be ferromagnetic, so that as current is passed through a wire coil that surrounds the plunger, the resulting magnetic force can move the plunger. Because of this aspect of its functionality, the plunger is sometimes referred to as an “armature”. In typical configurations, a spring and/or fluid pressure biases the plunger to a “normal” position when the coil is not energized.
Hydraulic pressure control actuators typically have a fluid pressure source connected to an inlet port and provide pressure control or flow output to an outlet port for discharge to a sump or pressure source return. Two primary poppet-type actuator configurations exist, a “pro-seal”, in which the inlet pressure creates a biased hydraulic force on a poppet acting to seal at a mating seat contact surface, and a “contra-seal”, where the inlet pressure acts to break the seal at the actuator seat. Contra-seal configurations are preferred for normally open valves, inasmuch as the magnetic force created by the solenoid does not act against the supply pressure when the primary air gap is largest and, therefore the solenoid is producing the least magnetic forces. Pro-seal configurations are preferred for normally closed applications, inasmuch as the supply pressure will assist to keep the valve closed.
Using a contra-seal configuration for normally closed valves and pro-seal configuration for normally open valves requires the implementation of spring preloads that must surpass the hydraulic forces acting on the poppet, thus requiring larger solenoid magnetic packages. One of the limitations to exercise this rule of thumb is the customer-porting configuration requirement. When the supply pressure at the inlet port feeds radially into the poppet chamber and exhausts axially opposite of the poppet chamber in a normally open valve, traditional valve configurations will automatically create the undesired pro-seal pressure condition.
Known actuators employed in applications such as automotive transmission shift control have utilized a ball valve member disposed in the valving chamber with the ball moved with respect to a valve seat by an operating rod connected to the solenoid armature for controlling flow from the supply port to the valving chamber. However, actuators of this type have encountered instability and flutter of the ball valve member upon exposure to hydraulic transients in the system and vibration encountered by the transmission. Efforts to counteract such instability and valve flutter in solenoid operation transmission shift control valves have utilized stiffer bias springs acting against the ball valve. This results in greater force and increased power requirements for the solenoid. For applications requiring a plurality of shift control valves, a prohibitively high power consumption for the actuators is the result.
The aforesaid solenoid valves employing a ball valve member have been found particularly susceptible to flutter when the ball valve member is in a position to substantially restrict the flow or near the closed position when the flow velocity is increased over the valve seat. It therefore has long been desired to provide a simple and relatively low cost way or means of reducing or eliminating flutter in a solenoid operated pressure control valve and particularly valves of the type employing solenoid operation off of low voltage power supply widely employed in motor vehicle applications.